5 IntroductionSeveral natural disasters have occurred since the time of biblical Noah up till now. These natural disasters have taken various forms such as; flooding, earthquake, volcanic eruption tsunamis, tornadoes, landslides, hurricane, among others.Flooding was defined by Hague: 1997 as “a natural hazard which displaces people by destroying their land, houses and other tangible goods and assets” [2]

6 Problem StatementWithin the last decades, Accra has experienced periodic floods. Between 1955 and 1997, about GH¢300 billion worth of properties has been destroyed, 100 lives have been lost either during the flood period or after the floods and 10,000 people have been displaced from their homes [8]. Against this background, the research seems necessary.

7 JustificationThe Government of Ghana has signed a contract (US$ 660 million) with the Conti Group of Companies from the USA on a five year project to tackle the flooding situation in Accra [7].

8 Research ObjectivesTo assess the natural and manmade activities that causes flood in Accra.To examine suitable structural measures that can be to undertaken to reduce and manage flood impacts in Accra.Propose a mitigation approach to manage flood impacts using Integrated Urban Flood Risk Management for The 21st Century.

9 Natural Disaster in Ghana from 1900 to 2014 Total Affected (persons)№ of EventsKilledTotal Affected (persons)Damage (US$)Drought3-12,512,000100,000Flood174093,884,990780,500,000Epidemic1987533,799Wildfire141500EarthquakeECONOMIC IMPACT OF FLOODING SHOWED IN THE FIGURESource: EM-DAT: The OFDA/CRED International Disaster (Adapted)

10 Profile of the Study AreaAccra is the capital city of GhanaPopulation: 2 millionLand mass: 1,261km2Source:

11 Drainage System & Characteristics 1Accra consists of eight drainage basins with Characteristics of lowlands, and hilly areas that runs out into the sea. As a result of these basins, storm water runs out from the city through it.

13 Drainage System & Characteristics 2According to waterworld, the design capacity of these basins is based on a 25-year return period: which means that the maximum rainfall reoccurs in 25 years [3].

14 Drainage System & Characteristics 3Over a period from 1970 – 2008, the average annual rainfall is 756 mm with about km3/year as the total amount of rain that falls in Accra within one year with a rainfall intensity variations of 203 mm/h [6].A rainfall intensity variations of 203 mm/h may or may not be reached for short periods of rainfall [23]

15 Early Warning SignsThe Ghana Meteorological Service relays information to the Accra Metropolis through national television, local radio stations and newspapers to highlight impending storm that would hit the metropolis but unfortunately, the intensity and the extent of flash floods are always not predicted [6].Unfortunately, Mechanisms of evacuation has never being implemented apart from the formal mechanisms of early warning signs through the media

16 Traditional Flood Management PossibilitiesThere are a number of different ways to categorize such flood management interventions. These flood management interventions can be either structural or non-structural; physical and institutional; implemented before, during and after the flood and these categories are interwoven [2].Conventionally, management of floods in Accra management has in essence been a struggle for successive governments in Ghana as strategies to combat this havoc has being problematic: new flood projects are implemented after a severe flood.2. Flood management practices have mostly concentrated on reducing flooding and decreasing the exposure to flood damage through a range of interventions.

18 Source: Guidelines for Planning Authorities: 20093.1 Erosion and Sedimentation In Accra where roads are not tarred, gullies and erosion are evident on road surfaces and the soil between buildings as a result of this, floodwater is stopped from entering roadside drains where they are provided. Problems associated with reduced capacity as erosion results in a high delivery of sediments from some urbanized area around the catchment.3.2 Improper SettlementsSome buildings in certain towns in Accra are positioned close to rivers and drains, whilst others are built only a few meters away from the stream channel or even across natural watercourses which results in increasing the risk of these settlements to flooding.3.3 Drainage Capacity Current drains like the Korle Lagoon are often clogged with refuse and silt which results in reduced capacity of the river or stream channels leading to flooding.3.4 Improper Waste Management PracticesImproper waste management practices in Accra and the incidence of flooding in the city are correlated.3.5 Urbanization Increasing Urbanization and its related activities have impacted negatively on the drainage systems in Accra. Development of residential buildings and paved roads increases the impermeability of the catchment areas giving rise to quicker catchment response to rainfall and increased runoff.Source: Guidelines for Planning Authorities: 2009

22 Research Analysis and DiscussionWater run-off with the basins in Accra was deduced using the modified rational model by Viessman & Lewis, 1996; and Mannaerts, 1996 to calculate individual discharge for each section in the entire catchment areas. i.e. Qp= 0.278×Cs×C×i×AA secondary data on the size of the basins in Accra, the run-off coefficient, storage coefficient and the rainfall intensity was derived from Ghana Meteorological service. From these data. Water run-off with the basins in Accra was deduced using the modified rational model by Viessman & Lewis, 1996; and Mannaerts, 1996 to calculate individual discharge for each section in the entire catchment areas.I.e. Qp= 0.278×Cs×C×i×A [33], [34]In the calculation of the discharge of each basin, the formula below was employed;Qp= 0.278×Cs×C×i×A [33], [34]Where: Qp= run-off rate (m3/s),C= Run-off Co-efficient,Cs= Storage Coefficient,i= Rainfall Intensity (mm/hr) andA= Area of Drainage (Km2)Run-off coefficient of urban areas ranges between 0.7 and 0.95.

23 Research Analysis and Discussion 3From the figure above, it can be deduced that as the area increases, peak discharge also increases.This is because, large drainage basins catches more precipitation so have a higher peak discharge compared to smaller basins. Smaller basins generally have shorter lag time because precipitation does not have as far distance to travel.This is the reason why Middle Sakumo basin continues to experience that highest floods in Accra. As a result of increased urbanization, the drainage basins, the run-off coefficient, as well as the peak run-off will increase

24 Research Analysis and Discussion 2In Ghana, raining season starts from April and ends in July with heavy rainfall and thunderstorms mostly in May. High rainfall intensities can have an effect on the storm hydrograph.Heavy storms result in more water entering the drainage basin which results in a higher discharge leading to flood over a long period of time.

25 Integrated Flood Risk Management Approach 1Global Water Partnership (GWP), defines Integrated Water Resources Management as ‘a process which promotes the coordinated management and development of water, land and related resources, in order to maximize the resultant economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystems’ [4]

26 Integrated Flood Risk Management Approach 2An Integrated Flood Management plan should address the following six key elements that follow logically for managing floods in the context of an IWRM approach:• Manage the water cycle as a whole;• Integrate land and water management;• Manage risk and uncertainty;• Adopt a best mix of strategies;• Ensure a participatory approach; and• Adopt integrated hazard management approaches.IN OTHER WORDS, ANY FLOOD MANAGEMENT PROJECT WITOUT THE INTEGRATED FLOOD RISK MANAGEMENT APPROACH LACKS MERIT.

29 Dikes, levees and flood embankments High flow diversions STRATEGYOPTIONSReducing FloodingDams and reservoirsDikes, levees and flood embankmentsHigh flow diversionsCatchment managementChannel improvementsReducing susceptibility to DamageFloodplain regulationDevelopment and redevelopment policiesDesign and location of facilitiesHousing and building codesFlood proofingFlood forecasting and warningMitigating the impacts of floodingInformation and educationDisaster preparednessPost-flood recoveryFlood insurancePreserving the Natural Resources of Flood PlainsFloodplain zoning and regulationintegrated flood risk management interventions incorporates a combination of structural and non-structural; physical and institutional; and these must be implemented before, during and after the flood.Source: Adapted from WMO: 2006

30 ConclusionFlooding as a natural disaster cannot be eradicated in Accra but however, its effect can be minimized by undertaking the Integrated Flood Management approach which promotes the coordinated management and development of water, land and related resources, in order to maximize the resultant economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystems.

31 RecommendationsThere should be improved collection of waste and disposal, de-silting gutters, river channels, and culverts that are frequently taken up by solid waste to improve the hydraulic performance of drains and increase carrying capacities in order to reduce peak discharge.There should be an enforcement of building regulations that prevent people from building in flood prone areas and floodplains to avoid flooding.